Glen Peters Profile picture
Aug 8, 2018 10 tweets 4 min read Twitter logo Read on Twitter
A #HothouseEarth THREAD

The standard headline & interpretation: We are doomed, the Earth's climate will runaway to 4-5°C even if we slash emissions.

Well, that is not what the paper says (actually, it is a Perspective), & I don't see this framing as particularly helpful!
The paper does not seem to define "Hothouse Earth", this seems to come from the press material? I don't see much on 4-5°C or 10-60m in the paper, if so, it is very indirect?
The paper "explores" if we "could" instigate feedbacks, they "could" cascade, & they "could" lead to a hothouse earth (whatever that is). "We cannot exclude" this happening at 1.5-2°C. The closing paragraph says we should investigate these issues! pnas.org/content/early/…
Nothing necessarily new here, except a new hashtag. @bobkopp gives a good summary
I like a good infographic, but worth noting that this is illustrative & we don't know the depth on the stability axis. We certainly don't know if the Earth is about to roll into the Hothouse. Maybe it is, we just don't know.
There are a range of feedbacks that may be triggered at different temperatures, & may operate on different timescales (decades, centuries). They may interact. Even at 1.5-2°C "we cannot exclude the risk that a cascade of feedbacks [lead] irreversibly onto a “Hothouse Earth”".
Carbon cycle feedbacks "could" lead to an addition 0.5°C if we follow a 2°C pathway. Could be bigger, could be smaller. Understanding these feedbacks is important yes, but the implication is not "hothouse earth imminent even with emission reductions" (as in some media)
One unfortunate aspect was the "emission reductions are not enough", which seems mainly to come from the press material? The intention was "emissions reductions AND carbon dioxide removal needed". The first bullet on the "highlights" also misleads on this?
stockholmresilience.org/research/resea…
After reading the headlines & news stories, my initial reaction was "well, we should give up & focus on adaptation". Was that intended? Scientists should be straight shooters & say the way it is, but after reading the Perspective & the media, they don't really seem connected...
All I can ask, is for people to go & read the paper. It is currently freely accessible pnas.org/content/early/….

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More from @Peters_Glen

Sep 26, 2018
THREAD (to get you prepared for the #IPCC Special Report on 1.5°C #SR15)

What are the origins of 1.5°C?

cicero.oslo.no/en/understandi…
1987: President of the Maldives: "We know, & yet we keep delaying action. The time for just talking is over."
1988: James Hanson testified "99% confidence"
1988: The #IPCC is born
1990: IPCC First Assessment Report (FAR)
1990: Alliance of Small Island States (AOSIS)
1992: UNFCCC "to prevent dangerous anthropogenic interference with the climate system"
1997: Kyoto Protocol
2007: Bali Road Map gives new hope
2008: A limit well below 1.5°C (Tuvalu, AOSIS)
2008: 1.5°C to stay alive
2009: Copenhagen Accord enshrined 2°C in climate politics
Read 5 tweets
Aug 31, 2018
Impressive new study on the carbon intensity of crude oil production by field. Average life-cycle emissions are 10.3gCO₂-eq/MJ or 1.7GtCO₂-eq (5% global energy GHG emissions), with huge variation by field / country. 1/5
science.sciencemag.org/content/361/64… ($)
Flaring (red), heavy oil (blue), or both (yellow) are key factors increasing emissions. Flaring is 22% of average weighted carbon intensity, but much higher in some places (over 50%). Heavy oil can be very emission intensive, but not always. 2/5
This will excite Norway: "Although some giant North Sea offshore fields have shown rapidly increasing per-barrel emissions due to depletion, they have low upstream GHG intensities when compared to many other global oil fields." 3/5
Read 6 tweets
Aug 28, 2018
What is the role of oil in a 2°C world?

THREAD on my presentation at #ONS2018 #CentreCourt (Monday), where I (try to) explain why there is potentially space for some new oil & what constrains the amount 1/

slideshare.net/GlenPeters_CIC…
It is important to remember, that every molecule of CO₂ that enters the atmosphere causes the temperature to increase. To stop temperature rising, either stop emitting CO₂ or, if you must, take out what you put in. 2/
Because it is unlikely we can get to zero emissions in 10-20 years (1.5°C) or 30-40 years (2°C), we have to remove CO₂ from the atmosphere. The more removed, the less radical the short-term reductions. Radical mitigation AND CO₂ removal is key. 3/
Read 13 tweets
Jun 20, 2018
THREAD on the climate sensitivity (& carbon budgets)...

After decades of research, the equilibrium climate sensitivity has remained fairly close to 3°C for a doubling of pre-industrial CO₂ concentrations.

carbonbrief.org/explainer-how-…
The range has remained stubbornly wide (1.5°C-4.5°C), despite many individual studies claiming to narrow it (particularly recent instrumental-based methods). Though, @AndrewDessler could argue that in the 1970's the range was underestimated & today it is overestimated (maybe).
Most methods have a similar range, but instrumental methods are certainly lower. Many reasons why the instrumental record may be low (aerosols, variability, temperature estimates, ocean heat content, etc, etc).
Read 9 tweets
Jun 19, 2018
This thread seems to get two things wrong
1. Emissions need to be as close as possible to zero AND CO₂ removal is needed in addition (it is not either/or)
2. Mitigation is currently FAR cheaper than removal (removal may help costly mitigation, like air to fuels for aviation)
If CO₂ removal was used to just offset existing emissions (instead of reducing emissions), it is far cheaper to deploy energy efficiency, solar, batteries, CCS, etc, then recapture emissions directly from air (expensive). Even if social cost was $80/tCO₂, still take cheapest?
In emission scenarios (shown for 1.5°C), CO₂ removal has two roles:
* Small: Offset hard to mitigate sectors (the brown does not go to zero, need CO₂ removal)
* Big: Offset earlier emissions (already emitted too much, which gets worse if we don't mitigate drastically today)
Read 5 tweets
Jun 19, 2018
THREAD

What are climate scenarios?

We use scenarios to explore the consequences of uncertainties (social, political, technical, climate).

cicero.oslo.no/en/posts/news/…
Climate scenarios are generally separated into two categories:
1. Transition risks related to the transition to a lower-carbon economy
2. Physical risks related to the physical impacts of climate change
Both types depend on different tools & methods
Scenarios should cover a range of possible outcomes. In practice, scenarios often focus on particular outcomes (levels of radiative forcing, policy characteristics, technology portfolios, behavioural change) meaning that a large part of the scenario space can be left unexplored.
Read 8 tweets

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